Gas supply device for internal combustion engine and control method for the same

ABSTRACT

A gas supply device is equipped with an oxygen enrichment membrane module, a pump portion, and an electronic control unit. The electronic control unit performs oxygen enrichment control for merging the air supplied to a first space from a second space through the oxygen enrichment membrane and containing a higher concentration of oxygen than an atmosphere with the atmosphere that has flowed into the first space and supplying the merged air and atmosphere to a combustion chamber of the cylinders by driving the pump portion, and nitrogen enrichment control for discharging air containing a higher concentration of oxygen than the atmosphere to the second space from the first space through the oxygen enrichment membrane, producing air containing a higher concentration of nitrogen than the atmosphere in the first space, and supplying the air containing the higher concentration of nitrogen to the combustion chamber by driving the pump portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

The disclosure of Japanese Patent Application No. 2017-100114 filed onMay 19, 2017 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

The disclosure relates to a gas supply device for an internal combustionengine that reforms an atmosphere (air) into “oxygen-enriched aircontaining a higher concentration of oxygen than the atmosphere” or“nitrogen-enriched air containing a lower concentration of oxygen thanthe atmosphere”, and that supplies the reformed air to a combustionchamber.

2. Description of Related Art

As described in, for example, Japanese Patent Application PublicationNo. 2016-166602 (JP 2016-166602 A), one conventionally known gas supplydevice of this kind (hereinafter referred to as “a conventional device”)for an internal combustion engine is equipped with a supercharger (aturbocharger), a gas separation device, a first gas storage device, asecond gas storage device, a first valve, a second valve, and a thirdvalve. The gas separation device includes a membrane structure (anoxygen enrichment membrane) that separates the atmosphere (compressedair) pressurized by a compressor of a supercharger into oxygen-enrichedair and nitrogen-enriched air.

The first gas storage device stores the oxygen-enriched air obtainedthrough separation by the gas separation device. The first valvecontrols the amount of oxygen-enriched air supplied to a combustionchamber from the first gas storage device. The second gas storage devicestores the nitrogen-enriched air obtained through separation by the gasseparation device. The second valve controls the amount ofnitrogen-enriched air supplied to the combustion chamber from the secondgas storage device. The third valve controls the amount of compressedair supplied to the combustion chamber from the compressor withoutpassing through the gas separation device.

SUMMARY

In order to separate the atmosphere into oxygen-enriched air andnitrogen-enriched air through the use of an oxygen enrichment membrane,a difference in pressure (hereinafter referred to as “a membranedifferential pressure”) needs to be created between two spaces that areseparated from each other by the oxygen enrichment membrane. Theconventional device generates the membrane differential pressure byintroducing “the atmosphere pressurized by the supercharger” into one ofthe two spaces.

However, when the internal combustion engine is operated in “anon-supercharging range where the supercharger cannot substantiallycarry out supercharging (compression and pressurization of theatmosphere)”, the conventional device cannot generate a sufficientlyhigh membrane differential pressure. That is, when the internalcombustion engine is operated in the non-supercharging range, theconventional device cannot supply oxygen-enriched air ornitrogen-enriched air to the combustion chamber.

The disclosure has been made in view of the above-mentioned problem.That is, the disclosure provides a gas supply device for an internalcombustion engine (hereinafter referred to also as “a device of thedisclosure”) and a control method therefor that can reform theatmosphere into “oxygen-enriched air or nitrogen-enriched air”independently of the operating state of the internal combustion engineand supply the reformed air into a combustion chamber.

Thus, according to one aspect of the disclosure, there is provided a gassupply device for an internal combustion engine. The gas supply deviceis equipped with an oxygen enrichment membrane module, a first pipeportion, a second pipe portion, a pump portion, and an electroniccontrol unit. The oxygen enrichment membrane module includes a housingand an oxygen enrichment membrane. A space in the housing is separatedinto a first space and a second space by the oxygen enrichment membrane.The first pipe portion constitutes a first air passage including one endfrom which an atmosphere can flow into the one end and the other endwhich communicates with the first space. The second pipe portionconstitutes a second air passage including one end which communicateswith the first space and the other end which communicates with acombustion chamber of the internal combustion engine. The pump portionis configured to raise a pressure in the second space by supplying thehigh-pressure atmosphere to the second space, and is configured to lowerthe pressure in the second space by discharging air in the second spaceto an outside of the housing from the second space. The electroniccontrol unit is configured to: (i) control a drive state of the pumpportion, (ii) supply air to the first space from the second spacethrough the oxygen enrichment membrane, by supplying the high-pressureatmosphere to the second space by driving the pump portion such that thepressure in the second space rises, a concentration of oxygen of the airbeing higher than a concentration of oxygen of the atmosphere, (iii)perform oxygen enrichment control that merges the air supplied to thefirst space with the atmosphere that has flowed into the first spacethrough the first air passage, and supplies the merged air andatmosphere to the combustion chamber through the second air passage, theconcentration of oxygen of the air being higher than the concentrationof oxygen of the atmosphere, and (iv) perform nitrogen enrichmentcontrol that discharges air to the second space from the first spacethrough the oxygen enrichment membrane, a concentration of oxygen of theair being higher than a concentration of oxygen of the atmosphere,produces air in the first space, a concentration of nitrogen of the airbeing higher than a concentration of nitrogen of the atmosphere, andsupplies the air containing the higher concentration of nitrogen to thecombustion chamber through the second air passage, by discharging theair in the second space to the outside of the housing from the secondspace by driving the pump portion such that the pressure in the secondspace falls.

According to another aspect of the disclosure, there is provided acontrol method for a gas supply device for an internal combustionengine. The gas supply device includes an oxygen enrichment membranemodule, a first pipe portion, a second pipe portion, and a pump portion.The oxygen enrichment membrane module includes a housing and an oxygenenrichment membrane. A space in the housing is separated into a firstspace and a second space by the oxygen enrichment membrane. The firstpipe portion constitutes a first air passage including one end fromwhich an atmosphere can flow into the one end and the other end whichcommunicates with the first space. The second pipe portion constitutes asecond air passage including one end which communicates with the firstspace and the other end which communicates with a combustion chamber ofthe internal combustion engine. The pump portion is configured to raisea pressure in the second space by supplying the high-pressure atmosphereto the second space, and is configured to lower the pressure in thesecond space by discharging air in the second space to an outside of thehousing from the second space. The control method includes: (i)controlling a drive state of the pump portion, (ii) supplying air to thefirst space from the second space through the oxygen enrichmentmembrane, by supplying the high-pressure atmosphere to the second spaceby driving the pump portion such that the pressure in the second spacerises, a concentration of oxygen of the air being higher than aconcentration of oxygen of the atmosphere, (iii) performing oxygenenrichment control that merges the air supplied to the first space withthe atmosphere that has flowed into the first space through the firstair passage, and supplies the merged air and atmosphere to thecombustion chamber through the second air passage, the concentration ofoxygen of the air being higher than the concentration of oxygen of theatmosphere, and (iv) performing nitrogen enrichment control thatdischarges air to the second space from the first space through theoxygen enrichment membrane, a concentration of oxygen of the air beinghigher than a concentration of oxygen of the atmosphere, produces air inthe first space, a concentration of nitrogen of the air being higherthan a concentration of nitrogen of the atmosphere, and supplies the aircontaining the higher concentration of nitrogen to the combustionchamber through the second air passage, by discharging the air in thesecond space to the outside of the housing from the second space bydriving the pump portion such that the pressure in the second spacefalls.

According to the gas supply device and the control method therefor asdescribed above, when oxygen enrichment control is performed, thehigh-pressure atmosphere is supplied to the second space by driving thepump portion such that the pressure in the second space rises. Thus, thedifference in pressure (the membrane differential pressure) that isneeded to cause the air containing the higher concentration of oxygenthan the atmosphere to flow into the first space through the oxygenenrichment membrane is created between the first space and the secondspace.

When nitrogen enrichment control is performed, the air in the secondspace is discharged to the outside of the housing from the second spaceby driving the pump portion such that the pressure in the second spacefalls. Thus, the difference in pressure (the membrane differentialpressure) that is needed to discharge the air containing the higherconcentration of oxygen than the atmosphere to the second space throughthe oxygen enrichment membrane is created between the first space andthe second space.

Accordingly, even when the internal combustion engine is in thenon-supercharging range, oxygen-enriched air and nitrogen-enriched aircan be supplied to the combustion chamber by driving the pump portion.

Besides, in the gas supply device according to the disclosure, thehousing may include a first communication hole and a secondcommunication hole. The first communication hole may establishcommunication between the first space and the other end of the first airpassage. The second communication hole may establish communicationbetween the first space and the one end of the second air passage. Also,the first communication hole and the second communication hole may beprovided at positions that are opposed to each other. The first pipeportion may be connected to the housing such that the other end of thefirst air passage communicates with the first communication hole. Thesecond pipe portion may be connected to the housing such that the oneend of the second air passage communicates with the second communicationhole.

According to the gas supply device as described above, theaforementioned first communication hole and the aforementioned secondcommunication hole are formed at positions that are opposed to eachother. Therefore, the atmosphere passing through the oxygen enrichmentmembrane module toward the combustion chamber is in contact with theoxygen enrichment membrane over a large area or for a long time.Accordingly, the atmosphere passing through the oxygen enrichmentmembrane module toward the combustion chamber can be efficientlyreformed into oxygen-enriched air or nitrogen-enriched air.

Besides, the gas supply device as the device of the disclosure may beequipped with a check valve that is configured to discharge the air inthe second space to the outside of the housing by opening when thepressure in the second space becomes equal to or higher than apredetermined valve-opening pressure.

According to the gas supply device as described above, when the pressurein the second space becomes equal to or higher than the predeterminedvalve-opening pressure, the check valve is opened, and the air in thesecond space is discharged to the outside. Accordingly, the possibilityof the partial pressure of oxygen in the air in the second spacebecoming excessively low can be reduced, so the air can be sufficientlyreformed into oxygen-enriched air.

Besides, the gas supply device as the device of the disclosure may beequipped with a third pipe portion that constitutes a third air passage,one end of the third air passage being connected to the pump portion,and a fourth pipe portion that constitutes a fourth air passage that isopened and closed by the check valve. Also, the housing may be equippedwith a third communication hole that establishes communication betweenthe second space and the third air passage, and a fourth communicationhole that establishes communication between the second space and thefourth air passage. Also, the third communication hole and the fourthcommunication hole may be provided at positions that are opposed to eachother. Also, the third pipe portion may be connected to the housing suchthat the other end of the third air passage communicates with the thirdcommunication hole, and the fourth pipe portion may be connected to thehousing such that the fourth air passage communicates with the fourthcommunication hole.

According to the gas supply device as described above, the thirdcommunication hole and the fourth communication hole are formed atpositions that are opposed to each other. Therefore, the atmosphereforce-fed from the pump portion is in contact with the oxygen enrichmentmembrane over a large area or for a long time. Accordingly, a largeamount of air containing a higher concentration of oxygen can besupplied to the first space, so the atmosphere passing through theoxygen enrichment membrane module toward the combustion chamber can beefficiently reformed into oxygen-enriched air.

In the gas supply device as the device of the disclosure, the oxygenenrichment membrane may assume a shape of a hollow tube with both endsurfaces of the hollow tube open, and may be disposed in such a manneras to connect the first communication hole and the second communicationhole to each other. Thus, a space inside the oxygen enrichment membranemay constitute the first space, and a space other than the first spacein the housing may constitute the second space. The housing may beprovided with the first communication hole, the second communicationhole, the third communication hole, and the fourth communication holesuch that a direction in which the third communication hole and thefourth communication hole are linked with each other becomes parallel toa surface perpendicular to a direction in which the first communicationhole and the second communication hole are linked with each other.

According to the gas supply device as described above, the direction inwhich the third communication hole and the fourth communication hole arelinked with each other is parallel to the surface perpendicular to thedirection in which the first communication hole and the secondcommunication hole are linked with each other. Accordingly, theatmosphere passing through the oxygen enrichment module can beefficiently reformed into oxygen-enriched air.

The gas supply device as the device of the disclosure may be furtherequipped with a compressor, a first throttle valve, and a secondthrottle valve. The compressor may be a compressor of a supercharger ofthe internal combustion engine that is disposed in the first pipeportion. The first throttle valve may be disposed in the first pipeportion between the compressor and the oxygen enrichment membranemodule, and may be configured to change a passage cross-sectional areaof the first air passage through a change in opening degree of the firstthrottle valve. The second throttle valve may be disposed in the secondpipe portion between the oxygen enrichment membrane module and thecombustion chamber of the internal combustion engine, and may beconfigured to change a passage cross-sectional area of the second airpassage through a change in opening degree of the second throttle valve.The electronic control unit may be configured to: in performing theoxygen enrichment control, (i) change the opening degree of the firstthrottle valve in accordance with an in-cylinder requested intake airflow rate as a flow rate of air requested of the combustion chamber ofthe internal combustion engine, and (ii) set the opening degree of thesecond throttle valve to an opening degree at a time when the secondthrottle valve is fully open. Also, the electronic control unit may beconfigured to: in performing the nitrogen enrichment control, (i) setthe opening degree of the first throttle valve to an opening degree at atime when the first throttle valve is fully open, and (ii) change theopening degree of the second throttle valve in accordance with thein-cylinder requested intake air flow rate.

According to the gas supply device as described above, when oxygenenrichment control is performed, the opening degree of the firstthrottle valve and the opening degree of the second throttle valve areset as described above. Therefore, the pressure in the first space ofthe oxygen enrichment membrane module is negative. Accordingly, themembrane differential pressure can be generated even without substantialpressurization by the pump portion, so oxygen-enriched air can besupplied with good energy efficiency.

Furthermore, according to the gas supply device as described above, whennitrogen enrichment control is performed, the opening degree of thefirst throttle valve and the opening degree of the second throttle valveare set as described above. Therefore, the pressure in the first spaceof the oxygen enrichment membrane module is positive. Accordingly, themembrane differential pressure can be generated without substantialdepressurization by the pump portion, so nitrogen-enriched air can besupplied with good energy efficiency.

In the gas supply device as the device of the disclosure, the electroniccontrol unit may be configured to: (i) stop driving the pump portion,(ii) set the opening degree of the first throttle valve to the openingdegree at the time when the first throttle valve is fully open, (iii)change the opening degree of the second throttle valve in accordancewith the in-cylinder requested intake air flow rate, and (iv) performnormal control for supplying the air flowing into the first space fromthe first air passage to the combustion chamber through the second airpassage, without reforming the air.

According to the gas supply device as described above, theaforementioned normal control is performed with the pump portion stoppedfrom being driven. Accordingly, the pump portion is prevented fromconsuming energy wastefully.

Moreover, the gas supply device as the device of the disclosure may befurther equipped with a fifth pipe portion and a third throttle valve.The fifth pipe portion may constitute a fifth air passage including oneend that communicates with a location between the compressor in thefirst air passage and the first throttle valve and the other end thatcommunicates with a location between the second throttle valve in thesecond air passage and the communication chamber. Also, the thirdthrottle valve may be disposed in the fifth pipe portion and change apassage cross-sectional area of the fifth air passage through a changein opening degree of the third throttle valve. The electronic controlunit may be configured to set the opening degree of the third throttlevalve to an opening degree at a time when the third throttle valve isfully closed, in performing the oxygen enrichment control or thenitrogen enrichment control. The electronic control unit may beconfigured to change the opening degree of the third throttle valve inaccordance with the in-cylinder requested intake air flow rate, inperforming the normal control.

According to the gas supply device as described above, when normalcontrol is performed, no air flows through the oxygen enrichmentmembrane module, so there is no pressure loss which would be causedduring the flow of air through the oxygen enrichment membrane module.Accordingly, no energy is wastefully consumed, so fuel economy can beimproved.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is an outline view of an internal combustion engine to which agas supply device for an internal combustion engine according to thefirst embodiment of the disclosure is applied;

FIG. 2A is an outline view of a longitudinal section of an oxygenenrichment membrane module shown in FIG. 1;

FIG. 2B is another outline view of the longitudinal section of theoxygen enrichment membrane module shown in FIG. 1;

FIG. 3A is an outline view showing the configuration of the oxygenenrichment membrane module;

FIG. 3B is a schematic view for illustrating a mechanism of an oxygenenrichment membrane;

FIG. 4 is a time chart for illustrating the outline of the operation ofthe gas supply device for the internal combustion engine according tothe first embodiment of the disclosure;

FIG. 5A is an outline view for illustrating the outline of the operationof the gas supply device for the internal combustion engine according tothe first embodiment of the disclosure;

FIG. 5B is another outline view for illustrating the outline of theoperation of the gas supply device for the internal combustion engineaccording to the first embodiment of the disclosure;

FIG. 5C is still another outline view for illustrating the outline ofthe operation of the gas supply device for the internal combustionengine according to the first embodiment of the disclosure;

FIG. 6 is a graph showing a relationship between a pressure in anextra-membrane space of the oxygen enrichment membrane module (anextra-membrane pressure) and a concentration of oxygen in theextra-membrane space of the oxygen enrichment membrane module (anextra-membrane oxygen concentration);

FIG. 7 is an outline view of an internal combustion engine to which agas supply device according to a reference example (a related art) ofthe present embodiment of the disclosure is applied;

FIG. 8 is a graph showing compositions, flow rates, and pressures ofintake air and the like at the time when the gas supply device accordingto the reference example (the related art) performs oxygen enrichmentcontrol;

FIG. 9 is a graph showing compositions, flow rates, and pressures ofintake air and the like at the time when the gas supply device for theinternal combustion engine according to the first embodiment of thedisclosure performs oxygen enrichment control;

FIG. 10 is a graph showing compositions, flow rates, and pressures ofintake air and the like at the time when the gas supply device for theinternal combustion engine according to the reference example performsnitrogen enrichment control;

FIG. 11 is a graph showing compositions, flow rates, and pressures ofintake air and the like at the time when the gas supply device for theinternal combustion engine according to the first embodiment of thedisclosure performs nitrogen enrichment control;

FIG. 12 is a flowchart showing a routine that is executed by a CPU of anECU of the gas supply device for the internal combustion engineaccording to the first embodiment of the disclosure;

FIG. 13 is an outline view of an internal combustion engine to which agas supply device for an internal combustion engine according to thesecond embodiment of the disclosure is applied; and

FIG. 14 is an outline view of an internal combustion engine to which agas supply device for an internal combustion engine according to thethird embodiment of the disclosure is applied.

DETAILED DESCRIPTION OF EMBODIMENTS

The gas supply device for the internal combustion engine according toeach of the embodiments of the disclosure will be described hereinafterwith reference to the drawings. Incidentally, like or equivalentcomponents are denoted by like reference symbols in all the drawings ofthe embodiments of the disclosure.

The configuration of the first embodiment of the disclosure will bedescribed. The gas supply device for the internal combustion engineaccording to the first embodiment of the disclosure (hereinafterreferred to as “a first gas supply device” in some cases) is applied to“an internal combustion engine 10 shown in FIG. 1”, which is mounted ina vehicle (not shown). The internal combustion engine 10 is amulti-cylinder (in-line four-cylinder in the present embodiment of thedisclosure), four-cycle, and reciprocating piston-type diesel engine.Incidentally, the internal combustion engine 10 may be a gasolineengine. The internal combustion engine 10 includes an engine bodyportion 20, an intake system 40, and an exhaust system 50.

The engine body portion 20 includes a body including a cylinder block(not shown), a cylinder head (not shown), a crankcase (not shown), andthe like. Four cylinders 22 are formed in the body. Fuel injectionvalves (injectors) (not shown) are disposed in upper portions of thecylinders 22 respectively. The fuel injection valves open in response toa command of an electronic control unit (an engine ECU) 70 that will bedescribed later, and directly inject fuel into the cylinders 22respectively.

The intake system 40 includes an intake manifold 41, a surge tank 42, anintake pipe 43 including a first pipe portion 43 a and a second pipeportion 43 b, an air cleaner 44 a, a compressor 45 a of a turbocharger45, an intercooler 46, a first throttle valve 47 a, a first throttlevalve actuator 47 b, an oxygen enrichment membrane module 48, a secondthrottle valve 49 a, and a second throttle valve actuator 49 b.

The intake manifold 41 is constituted of a plurality of branch-likeconduits that are connected to the cylinders 22 respectively in a mannerenabling communication. Each of these branch-like conduits is connectedat one end thereof to the surge tank 42 as an assembly portion of theseconduits, and is connected at the other end thereof to each of thecylinders 22. Furthermore, the surge tank 42 communicates with thesecond pipe portion 43 b of the intake pipe 43. The intake manifold 41,the surge tank 42, and the intake pipe 43 constitute an intake passage.Incidentally, the intake passage that is constituted by the first pipeportion 43 a upstream of the oxygen enrichment membrane module 48 willbe referred to also as “a first air passage” for the sake ofconvenience. The intake passage that is constituted by the second pipeportion 43 b downstream of the oxygen enrichment membrane module 49 willbe referred to also as “a second air passage” for the sake ofconvenience.

In the intake pipe 43, an air cleaner 44 a, a compressor 45 a, anintercooler 46, a first throttle valve 47 a, an oxygen enrichmentmembrane module 48, and a second throttle valve 49 a are sequentiallydisposed (interposed), downstream along the flow of intake air indicatedby an arrow a1. Furthermore, the oxygen enrichment membrane module 48 isalso disposed in an auxiliary conduit 61 including a third pipe portion61 a and a fourth pipe portion 61 b. In concrete terms, the oxygenenrichment membrane module 48 is disposed at a merging portion of theintake pipe 43 and the auxiliary conduit 61. In the auxiliary conduit61, an air cleaner 44 b, a well-known rotary pump 62, an oxygenenrichment membrane module 48, and a check valve 63 are sequentiallydisposed (interposed), downstream along the flow of auxiliary airindicated by an arrow a2.

The auxiliary conduit 61 constitutes an air passage through which airpasses (hereinafter referred to as “an external route” in some cases).Incidentally, an air passage that is constituted by the third pipeportion 61 a upstream of the oxygen enrichment membrane module 48 willbe referred to also as “a third air passage” for the sake ofconvenience. Incidentally, an air passage that is constituted by thefourth pipe portion 61 b downstream of the oxygen enrichment membranemodule 48 will be referred to also as “a fourth air passage” for thesake of convenience.

When being positively rotated, the rotary pump 62 ejects pressurizedauxiliary air downstream of the rotary pump 62, and thereby force-feedsthe auxiliary air to the oxygen enrichment membrane module 48 throughthe third air passage. Furthermore, when being reversely rotated, therotary pump 62 sucks and discharges auxiliary air from the oxygenenrichment membrane module 48 through the third air passage. The rotarypump 62 will be referred to also as “a pump portion” for the sake ofconvenience.

The check valve 63 is disposed in the external route “at a positiondownstream of the oxygen enrichment membrane module 48”. When thepressure of gas (air) flowing out from the oxygen enrichment membranemodule 48 is equal to or higher than a predetermined valve-openingpressure, the check valve 63 is open to allow the gas (air) to flow fromthe oxygen enrichment membrane module 48 to the check valve 63. In otherwords, when the pressure of gas (air) flowing out from the oxygenenrichment membrane module 48 is lower than the predeterminedvalve-opening pressure, the check valve 63 is closed to stop and preventthe gas (air) from flowing from the oxygen enrichment membrane module 48to the check valve 63. Accordingly, the check valve 63 also stops andprevents the gas (air) from flowing from the check valve 63 to theoxygen enrichment membrane module 48.

Each of the air cleaner 44 a and the air cleaner 44 b is a filteringdevice that removes foreign matters from auxiliary air. The compressor45 a and the turbine 45 b constitute the turbocharger 45. A rotary shaftof the turbine 45 b is coupled to a rotary shaft of the compressor 45 a.By receiving exhaust gas flowing through an exhaust passage, the turbine45 b rotates to thereby rotate the compressor 45 a. The air passingthrough the intake passage is compressed (supercharged) through rotationof the compressor 45 a.

The intercooler 46 is a cooling device for intake air that is providedbetween an outlet of the turbocharger 45 (the compressor 45 a) and theintake manifold 41. The intercooler 46 lowers the temperature of intakeair.

The first throttle valve 47 a adjusts the amount of air passing throughthe intake passage by making variable the opening cross-sectional areaof the intake passage in a region where the first throttle valve 47 a isdisposed. The first throttle valve actuator 47 b changes the openingdegree of the first throttle valve 47 a (hereinafter referred to as “afirst throttle valve opening degree”) in accordance with a command ofthe ECU 70. Incidentally, the first throttle valve 47 a will be referredto also as “a first valve” for the same of convenience, and the firstthrottle valve opening degree will be referred to also as “a first valveopening degree” for the sake of convenience. Furthermore, the firstthrottle valve actuator 47 b includes a first throttle opening degreesensor 47 c for detecting the first throttle valve opening degree.

The oxygen enrichment membrane module 48 reforms the atmosphere into“oxygen-enriched air or nitrogen-enriched air” as needed.Oxygen-enriched air contains a higher concentration of oxygen than theatmosphere, and contains a lower concentration of nitrogen than theatmosphere. Nitrogen-enriched air contains a higher concentration ofnitrogen than the atmosphere, and contains a lower concentration ofoxygen than the atmosphere. As shown in FIG. 2A, FIG. 2B, and FIG. 3A,the oxygen enrichment membrane module 48 is equipped with a casingportion 48 a and an oxygen enrichment membrane (a polymer membrane) 48b.

The casing portion 48 a is made of metal, and substantially assumes theshape of a cylinder. The interior of the casing portion 48 a is a space(a void). The casing portion 48 a is disposed (interposed) in the intakepipe 43 such that an axial direction of the casing portion 48 acoincides with an axial direction of the intake pipe 43.

A plurality of first communication holes 48 a 1 are formed through oneend surface of the casing portion 48 a. A plurality of secondcommunication holes 48 a 2 are formed through the other end surface ofthe casing portion 48 a. Each of the first communication holes 48 a 1and each of the second communication holes 48 a 2 are formed atpositions that are opposed to each other. That is, “one of the firstcommunication holes 48 a 1 and one of the second communication holes 48a 2” that are opposed to each other are formed such that their centralaxis coincides with a straight line parallel to the axial direction ofthe casing portion 48 a.

A third communication hole 48 a 3 is formed through a part of a lateralsurface of the casing portion 48 a. A fourth communication hole 48 a 4is formed through the other part of the lateral surface of the casingportion 48 a. The third communication hole 48 a 3 and the fourthcommunication hole 48 a 4 are formed such that their central axiscoincides with a straight line perpendicular to the axial direction ofthe casing portion 48 a, in such a manner as to be opposed to each otherin the vicinity of a center in the axial direction.

The oxygen enrichment membrane 48 b is a well-known membrane made of apolymer such as polyimide resin, silicon or the like (e.g., see JapanesePatent Application Publication No. 2007-113459 (JP 2007-113459 A) andJapanese Patent Application Publication No. 2013-32708 (JP 2013-32708A)). The oxygen enrichment membrane 48 b changes the concentration ofoxygen in air and the concentration of nitrogen in air, utilizing thefact that the permeation speed of oxygen molecules through the oxygenenrichment membrane 48 b is higher than the permeation speed of nitrogenmolecules through the oxygen enrichment membrane in the process ofdissolution, diffusion and desorption of the oxygen molecules andnitrogen molecules in air (the atmosphere) to the oxygen enrichmentmembrane 48 b.

The oxygen enrichment membrane 48 b assumes the shape of a hollowcylinder, and is formed such that both end surfaces thereof are open.One end surface of the oxygen enrichment membrane 48 b is disposed ineach of the first communication holes 48 a 1, and the other end surfaceof the oxygen enrichment membrane 48 b is disposed in each of the secondcommunication holes 48 a 2. That is, “each of the first communicationholes 48 a 1 and each of the second communication holes 48 a 2” that areopposed to each other are connected to each other by the tubular oxygenenrichment membrane 48 b.

Accordingly, each of the first communication holes 48 a 1 and each ofthe second communication holes 48 a 2 communicate with the hollow insidethe oxygen enrichment membrane 48 b. On the other hand, the space insidethe casing portion 48 a and outside the oxygen enrichment membrane 48 bcommunicates with each of the third communication hole 48 a 3 and thefourth communication hole 48 a 4. The space inside the casing portion 48a and outside the oxygen enrichment membrane 48 b will be referred tohereinafter as “an extra-membrane space” in some cases. In contrast, thespace inside the oxygen enrichment membrane 48 b will be referred to as“an intra-membrane space” in some cases. Incidentally, theintra-membrane space will be referred to also as “a first space” for thesake of convenience. The extra-membrane space will be referred to alsoas “a second space”.

The third communication hole 48 a 3 is connected to the auxiliaryconduit 61 (the third pipe portion 61 a) on the rotary pump 62 side, andcommunicates with an air passage (an external route) that is formed bythe auxiliary conduit 61. The fourth communication hole 48 a 4 isconnected to the auxiliary conduit 61 (the fourth pipe portion 61 b) onthe check valve 63 side, and communicates with the air passage (theexternal route) that is formed by the auxiliary conduit 61.

The pressure in the extra-membrane space can be raised (pressurization),and the pressure in the space can be lowered (depressurization), throughthe use of the rotary pump 62. In other words, the pressure in theextra-membrane space can be made higher or lower than the pressure inthe intra-membrane space, by the rotary pump 62. That is, a differencein pressure can be created between the intra-membrane space and theextra-membrane space, which are separated from each other by the oxygenenrichment membrane 48 b.

As described previously, the oxygen enrichment membrane 48 b can changethe concentration of oxygen in air and the concentration of nitrogen inair. In more concrete terms, as shown in FIG. 3B, when a difference inpressure is created across the oxygen enrichment membrane 48 b, “theoxygen molecules and nitrogen molecules” that are in contact with a highpressure-side (pressurization-side) surface of the oxygen enrichmentmembrane 48 b are dissolved to the oxygen enrichment membrane 48 b fromthe pressurization-side surface, diffused in the oxygen enrichmentmembrane 48 b, and then desorbed from a low pressure-side(depressurization-side) surface of the oxygen enrichment membrane 48 b.At this time, a permeation coefficient Z_(O2) of oxygen through theoxygen enrichment membrane 48 b is larger than a permeation coefficientZ_(N2) of nitrogen through the oxygen enrichment membrane 48 b.

Accordingly, oxygen molecules permeate the oxygen enrichment membrane 48b faster than nitrogen molecules. In other words, the amount of oxygenmolecules permeating the oxygen enrichment membrane 48 b from thehigh-pressure side and moving toward the low-pressure side per unit timeis larger than the amount of nitrogen molecules permeating the oxygenenrichment membrane 48 b from the high-pressure side and moving towardthe low-pressure side per unit time. Thus, the air that has permeatedthe oxygen enrichment membrane 48 b becomes oxygen-enriched air, and theair that has not permeated the oxygen enrichment membrane 48 b becomesnitrogen-enriched air. Incidentally, a permeation amount Q_(O2) ofoxygen through the oxygen enrichment membrane 48 b is expressed byEquation (1) shown in FIG. 3B. A permeation amount Q_(N2) of nitrogenthrough the oxygen enrichment membrane 48 b is expressed by Equation (2)shown in FIG. 3B.

The first gas supply device reforms the intake air supplied to theoxygen enrichment membrane module 48 into oxygen-enriched air containinga higher concentration of oxygen than the intake air andnitrogen-enriched air containing a lower concentration of oxygen(containing a higher concentration of nitrogen) than the intake air,through the use of the characteristics of this oxygen enrichmentmembrane 48 b. Then, the first gas supply device supplies one of theoxygen-enriched air and the nitrogen-enriched air (i.e., the reformedintake air) into each of combustion chambers of the cylinders 22.

In concrete terms, the first gas supply device positively rotates therotary pump 62 in reforming the intake air flowing into theintra-membrane space from the first communication holes 48 a 1 intooxygen-enriched air and discharging the oxygen-enriched air from thesecond communication holes 48 a 2. As a result, the pressure ofauxiliary air introduced into the extra-membrane space from the externalroute and the third communication hole 48 a 3 becomes higher than thepressure of intake air in the intra-membrane space. Accordingly, theauxiliary air in the extra-membrane space is separated into the airpermeating the oxygen enrichment membrane 48 b, discharged to theintra-membrane space and containing a high concentration of oxygen, andthe air remaining in the extra-membrane space and containing a highconcentration of nitrogen. Then, as shown in FIG. 2A, the air dischargedto the intra-membrane space and containing a high concentration ofoxygen is mixed with the intake air that has flowed into theintra-membrane space from the first communication holes 48 a 1. Thus,the intake air that has flowed into the intra-membrane space from thefirst communication holes 48 a 1 is reformed into oxygen-enriched air,and the oxygen-enriched air is discharged from the second communicationholes 48 a 2. The oxygen-enriched air is supplied to each of thecombustion chambers of the cylinders 22 through the intake pipe 43 (thesecond pipe portion 43 b) and the surge tank 42.

In contrast, the first gas supply device reversely rotates the rotarypump 62 in reforming the intake air flowing into the intra-membranespace from the first communication holes 48 a 1 into nitrogen-enrichedair, and discharging the nitrogen-enriched air from the secondcommunication holes 48 a 2. As a result, the pressure of intake airintroduced into the intra-membrane space from the first communicationholes 48 a 1 becomes higher than the pressure of auxiliary air in theextra-membrane space. Accordingly, as shown in FIG. 2B, the intake airin the intra-membrane space is separated into the air permeating theoxygen enrichment membrane 48 b, discharged to the extra-membrane spaceand containing a high concentration of oxygen, and the air remaining inthe intra-membrane space and containing a high concentration ofnitrogen. Thus, the intake air that has flowed into the intra-membranespace from the first communication holes 48 a 1 is reformed intonitrogen-enriched air, and the nitrogen-enriched air is discharged fromthe second communication holes 48 a 2. The nitrogen-enriched air issupplied to each of the combustion chambers of the cylinders 22 throughthe intake pipe 43 (the second pipe portion 43 b) and the surge tank 42.

Referring again to FIG. 1, the second throttle valve 49 a adjusts theamount of air passing through the intake passage by making variable theopening cross-sectional area of the intake passage in a region where thesecond throttle valve 49 a is disposed. The second throttle valveactuator 49 b changes the opening degree of the second throttle valve 49a (hereinafter referred to as “a second throttle valve opening degree”)in accordance with a command of the ECU 70. Incidentally, the secondthrottle valve 49 a will be referred to also as “a second valve” for thesake of convenience, and the second throttle valve opening degree willbe referred to also as “a second valve opening degree” for the sake ofconvenience. Furthermore, the second throttle valve actuator 49 bincludes a second throttle opening degree sensor 49 c for detecting thesecond throttle valve opening degree.

The exhaust system 50 includes an exhaust manifold 51, an exhaust pipe52, and the turbine 45 b of the turbocharger 45.

The exhaust manifold 51 includes “branch portions that are connected tothe cylinders 22 respectively” and “an assembly portion of these branchportions”. The exhaust pipe 52 is connected to the assembly portion ofthe exhaust manifold 51. The exhaust manifold 51 and the exhaust pipe 52constitute the exhaust passage. The turbine 45 b is disposed in theexhaust pipe 52.

The ECU 70 is an electronic circuit including a well-knownmicrocomputer, and includes a CPU, a ROM, a RAM, a backup RAM, aninterface and the like. The ECU 70 is connected to a group of sensorsthat will be mentioned below, and receives (has input thereto) signalsfrom these sensors. Furthermore, the ECU 70 delivers command (drive)signals to various actuators, and controls the internal combustionengine 10.

The ECU 70 is connected to the first throttle opening degree sensor 47 cand the second throttle opening degree sensor 49 c. The first throttleopening degree sensor 47 c detects the first throttle valve openingdegree of the first throttle valve 47 a, and outputs a signalrepresenting a first throttle valve opening degree TA1. The secondthrottle opening degree sensor 49 c detects the second throttle valveopening degree of the second throttle valve 49 a, and outputs a signalrepresenting a second throttle valve opening degree TA2.

Furthermore, the ECU 70 is connected to intake pipe pressure sensors 75a to 75 d, an auxiliary conduit pressure sensor 75 e, an oxygenconcentration sensor 76, an engine rotational speed sensor 77, a liquidtemperature sensor 78, and an accelerator pedal operation amount sensor79.

The intake pipe pressure sensor 75 a outputs a signal representing apressure P1 of intake air in the intake passage downstream of theintercooler 46 and in the intake pipe 43 upstream of the first throttlevalve 47 a. The intake pipe pressure sensor 75 b outputs a signalrepresenting a pressure P2 in the intake passage downstream of the firstthrottle valve 47 a and in the intake pipe 43 upstream of the oxygenenrichment membrane module 48. The intake pipe pressure sensor 75 coutputs a signal representing a pressure P3 of intake air in the intakepassage downstream of the oxygen enrichment membrane module 48 and inthe intake pipe 43 upstream of the second throttle valve 49 a. Theintake pipe pressure sensor 75 d outputs a signal representing apressure P4 of intake air in the intake passage downstream of the secondthrottle valve 49 a and in the intake pipe upstream of the surge tank42. The auxiliary conduit pressure sensor 75 e outputs a signalrepresenting a pressure P5 in the external route downstream of therotary pump 62 and in the auxiliary conduit 61 upstream of the oxygenenrichment membrane module 48.

The oxygen concentration sensor 76 outputs a signal representing aconcentration Oair of oxygen in the intake air (i.e., the atmosphere)introduced into the intake passage through the air cleaner 44 a.

The engine rotational speed sensor 77 measures a rotational speed (anengine rotational speed) NE of the internal combustion engine 10, andoutputs a signal representing this engine rotational speed NE.

The liquid temperature sensor 78 is disposed in a cylinder block portionof the engine body portion 20. The liquid temperature sensor 78 measuresa temperature (a cooling liquid temperature THW) of coolant for coolingthe engine body portion 20, and outputs a signal representing thiscooling liquid temperature THW.

The accelerator pedal operation amount sensor 79 detects an operationamount (an accelerator depression amount) of an accelerator pedal 79 aof the vehicle, and outputs a signal representing an accelerator pedaloperation amount AP.

Outline of Operation

Next, the outline of the operation performed by the first gas supplydevice will be described. The first gas supply device changes theconcentration of oxygen (and the concentration of nitrogen) in theintake air supplied into each of the combustion chambers, in accordancewith the operating state of the internal combustion engine 10.

In concrete terms, the ECU 70 determines a target value of theconcentration of oxygen (i.e., a target oxygen concentration Otg) in theintake air supplied into each of the combustion chambers of thecylinders 22, based on the operating state of the internal combustionengine 10. The ECU 70 compares “the concentration Oair of oxygen inintake air (the atmosphere)” acquired by the oxygen concentration sensor76 with “the target oxygen concentration Otg”.

Incidentally, the concentration Oair of oxygen in intake air (theatmosphere) acquired by the oxygen concentration sensor 76 will bereferred to hereinafter as “the detected oxygen concentration Oair”. Theintake air eventually supplied to each of the cylinders 22 will bereferred to as “cylinder intake air”. The intake air on the verge offlowing into the oxygen enrichment membrane module 48 through the intakepipe 43 will be referred to as “enrichment membrane inflow air”. The airincluding the same composition as the atmosphere will be referred to as“normal air”. The throttle valve opening degree at the time when thefirst throttle valve 47 a is fully open will be referred to as “a firstfull-admission opening degree”. The throttle valve opening degree at thetime when the second throttle valve 49 a is fully open will be referredto as “a second full-admission opening degree”.

When the detected oxygen concentration Oair is equal to the targetoxygen concentration Otg, the ECU 70 performs “normal control” forsupplying enrichment membrane inflow air to each of the cylinders 22 ascylinder intake air, without changing the concentration of oxygen inenrichment membrane inflow air by the oxygen enrichment membrane module48. When the detected oxygen concentration Oair is lower than the targetoxygen concentration Otg, the ECU 70 performs “oxygen enrichmentcontrol” for raising the concentration of oxygen in cylinder intake airby raising the concentration of oxygen in enrichment membrane inflow airby the oxygen enrichment membrane module 48. Incidentally, when thedetected oxygen concentration Oair is lower than the target oxygenconcentration Otg, the ECU 70 generates an oxygen enrichment request.When the detected oxygen concentration Oair is higher than the targetoxygen concentration Otg, the ECU 70 performs “nitrogen enrichmentcontrol” for lowering the concentration of oxygen (raising theconcentration of nitrogen) in cylinder intake air, by lowering theconcentration of oxygen in enrichment membrane inflow air by the oxygenenrichment membrane module 48. Incidentally, when the detected oxygenconcentration Oair is higher than the target oxygen concentration Otg,the ECU 70 generates a nitrogen enrichment request.

For instance, in the example shown in FIG. 4, the detected oxygenconcentration Oair is equal to the target oxygen concentration Otgduring a period from a timing t0 to a time point immediately before atiming t1. Accordingly, during this period, neither an oxygen enrichmentrequest nor a nitrogen enrichment request is generated.

When neither an oxygen enrichment request nor a nitrogen enrichmentrequest is generated, the ECU 70 performs the following operation shownin FIG. 5A. (i) The ECU 70 stops the rotary pump 62. (ii) The ECU 70sets the first throttle valve opening degree TA1 of the first throttlevalve 47 a to “the first full-admission opening degree”. (iii) The ECU70 determines the target value of the pressure in the region where theintake pipe pressure sensor 75 d is disposed, as a target intakepressure Pim4, based on “the engine rotational speed NE and anin-cylinder requested intake air flow rate”. It should be noted hereinthat the in-cylinder requested intake air flow rate is a flow rate ofcylinder intake air requested of each of the cylinders 22. (iv) The ECU70 separately calculates the in-cylinder requested intake air flow ratebased on “the engine rotational speed NE and the accelerator pedaloperation amount AP”. (v) The ECU 70 controls the second throttle valveopening degree TA2 such that the pressure P4 of intake air detected bythe intake pipe pressure sensor 75 d coincides with the target intakepressure Pim4.

In this case, in the oxygen enrichment membrane module 48, nosubstantial difference in pressure is created between the intra-membranespace and the extra-membrane space. Therefore, as indicated by a blockB1 in FIG. 5A, enrichment membrane inflow air as normal air passesthrough the intra-membrane space without permeating the oxygenenrichment membrane 48 b, and is discharged to the intake passage of theintake pipe 43 from the second communication holes 48 a 2. Accordingly,enrichment membrane inflow air passes through the oxygen enrichmentmembrane module 48 and becomes cylinder intake air, with theconcentration of oxygen therein remaining unchanged. Incidentally, theair thus passing through the oxygen enrichment membrane module 48 anddischarged to the intake pipe 43 from the second communication holes 48a 2 will be referred to also as “discharge intake air” for the sake ofconvenience.

In the example shown in FIG. 4, the target oxygen concentration Otgbecomes high at the timing t1. As a result, the detected oxygenconcentration Oair becomes lower than the target oxygen concentrationOtg at the timing t1, so oxygen-enriched air is requested. That is, anoxygen enrichment request is generated at the timing t1. Thus, the ECU70 starts oxygen enrichment control at the timing t1.

In this case, the ECU 70 performs the following operation shown in FIG.5B. The ECU 70 (i) sets the second throttle valve opening degree TA2 ofthe second throttle valve 49 a to “the second full-admission openingdegree”. The ECU 70 (ii) determines the target value of the pressure inthe region where the intake pipe pressure sensor 75 b is disposed, as atarget intake pressure Pim2, based on the engine rotational speed NE andthe in-cylinder requested intake air flow rate. The ECU 70 (iii)controls the first throttle valve opening degree TA1 of the firstthrottle valve 47 a such that the pressure P2 of intake air detected bythe intake pipe pressure sensor 75 b coincides with the target intakepressure Pim2. The ECU 70 (iv) determines a target membrane differentialpressure Pd based on the in-cylinder requested intake air flow rate andthe target oxygen concentration Otg. In this case, the target membranedifferential pressure Pd is a positive value. The ECU 70 (v) sets atarget pump pressure Ppump as a target value of the pressure ofauxiliary air (i.e., a target value of the pressure in theextra-membrane space) to a pressure (Pim2+Pd) obtained by summating thetarget intake pressure Pim2 and the target membrane differentialpressure Pd. The ECU 70 (vi) positively rotates the rotary pump 62 suchthat the pressure P5 of auxiliary air force-fed by the rotary pump 62(the pressure P5 detected by the auxiliary conduit pressure sensor 75 e)coincides with the target pump pressure Ppump.

Thus, the pressure in the extra-membrane space coincides with the targetpump pressure Ppump (=Pim2+Pd), and the pressure in the intra-membranespace coincides with the target intake pressure Pim2. Accordingly, theextra-membrane space and the intra-membrane space become thehigh-pressure side and the low-pressure side respectively, so themembrane differential pressure Pd obtained by subtracting Pim2 fromPpump (=Ppump−Pim2>0) is generated.

As a result, as indicated by a block B2 in FIG. 5B, the auxiliary airsupplied to the extra-membrane space through the auxiliary conduit 61and the third communication hole 48 a 3 permeates the oxygen enrichmentmembrane 48 b and is discharged to the intra-membrane space. Theauxiliary air discharged to this intra-membrane space contains a higherconcentration of oxygen than the auxiliary air (normal air) that has notpermeated the oxygen enrichment membrane 48 b yet. On the other hand,the auxiliary air in the extra-membrane space contains a lowerconcentration of oxygen than normal air.

As a result, enrichment membrane inflow air is reformed intooxygen-enriched air, and the oxygen-enriched air obtained throughreformation is supplied to each of the cylinders 22 as cylinder intakeair (discharge intake air). This “control from the timing t1” is oxygenenrichment control.

As shown in FIG. 4, through this oxygen enrichment control, the membranedifferential pressure (P5−P2) rises toward the target membranedifferential pressure Pd (=Ppump (positive pressure)−Pim (negativepressure)>0), and the concentration Od of oxygen in each of dischargeintake air and cylinder intake air rises toward the target oxygenconcentration Otg, from the timing t1. Furthermore, the membranedifferential pressure (P5−P2) coincides with the target membranedifferential pressure Pd, and the concentration Od of oxygen in each ofdischarge intake air and cylinder intake air coincides with the targetoxygen concentration Otg, at and after the timing t2.

Incidentally, when the extra-membrane pressure P5 applied to the checkvalve 63 becomes equal to or higher than the predetermined valve-openingpressure as a result of the continuation of positive rotation of therotary pump 62 after the start of the above-mentioned oxygen enrichmentcontrol, the check valve 63 is opened. Thus, “the auxiliary aircontaining a high concentration of nitrogen and a low concentration ofoxygen” in the extra-membrane space is discharged to the outside (theatmosphere) through the fourth communication hole 48 a 4, and normal airflows into the extra-membrane space through the third communication hole48 a 3. Accordingly, as indicated by a graph of FIG 6, the concentrationof oxygen in the extra-membrane space is held equal to an O₂ lowerlimit. In consequence, the concentration of oxygen in the extra-membranespace does not fall too much. Therefore, a difference (a difference inpartial pressure) between the partial pressure of oxygen in theextra-membrane space and the partial pressure of oxygen in theintra-membrane space is held equal to or higher than a partial pressureneeded for permeation of the oxygen enrichment membrane 48 b by oxygen.

In the example shown in FIG. 4, the target oxygen concentration Otgbecomes low at a timing t3. As a result, at the timing t3, the detectedoxygen concentration Oair becomes higher than the target oxygenconcentration Otg, so nitrogen-enriched air is requested. That is, anitrogen enrichment request is generated at the timing t3. Thus, the ECU70 starts nitrogen enrichment control at the timing t3.

In this case, the ECU 70 performs the following operation shown in FIG.5C. The ECU 70 (i) sets the first throttle valve opening degree TA1 ofthe first throttle valve 47 a to “the first full-admission openingdegree”. The ECU 70 (ii) determines the target value of the pressure inthe region where the intake pipe pressure sensor 75 d is disposed, asthe target intake pressure Pim4, based on the engine rotational speed NEand the in-cylinder requested intake air flow rate. The ECU 70 (iii)controls the second throttle valve opening degree TA2 of the secondthrottle valve 49 a such that the pressure P4 of intake air detected bythe intake pipe pressure sensor 75 d coincides with the target intakepressure Pim4. The ECU 70 (iv) determines the target membranedifferential pressure Pd based on the in-cylinder requested intake airflow rate and the target oxygen concentration Otg. In this case, thetarget membrane differential pressure Pd is a negative value. The ECU 70(v) sets the target pump pressure Ppump as the target value of thepressure of auxiliary air (i.e., the target value of the pressure in theextra-membrane space) to a pressure (P1+Pd) obtained by summating “thepressure P1 immediately after the passage through the intercooler asdetected by the intake pipe pressure sensor 75 a” and “the targetmembrane differential pressure Pd”. Incidentally, in this case, thefirst throttle valve opening degree TA1 is equal to “the firstfull-admission opening degree”. Therefore, the pressure of enrichmentmembrane inflow air (i.e., the pressure in the intra-membrane space) andthe pressure P1 are substantially equal to each other. The ECU 70 (vi)reversely rotates the rotary pump 62 such that the pressure P5 ofauxiliary air force-fed by the rotary pump 62 (the pressure P5 detectedby the auxiliary conduit pressure sensor 75 e) coincides with the targetpump pressure Ppump. That is, the ECU 70 lowers the pressure in theextra-membrane space.

Thus, the pressure in the extra-membrane space coincides with the targetpump pressure Ppump (=P1+Pd). On the other hand, as describedpreviously, the pressure in the intra-membrane space is substantiallyequal to the pressure P1. Accordingly, the extra-membrane space and theintra-membrane space become the low-pressure side and the high-pressureside respectively, and the membrane differential pressure Pd(=Ppump−P1<0) obtained by subtracting P1 from Ppump is generated.

As a result, as indicated by a block B3 in FIG. 5C, the air supplied tothe intra-membrane space through the first communication holes 48 a 1permeates the oxygen enrichment membrane 48 b and is discharged to theextra-membrane space. The air discharged to this extra-membrane spacecontains a higher concentration of oxygen than the air (normal air) thathas not permeated the oxygen enrichment membrane 48 b yet. Accordingly,the air remaining in the intra-membrane space and flowing therethroughbecomes nitrogen-enriched air containing a lower concentration of oxygenthan normal air.

As a result, enrichment membrane inflow air is reformed intonitrogen-enriched air, and the nitrogen-enriched air obtained throughreformation is supplied to each of the cylinders 22 as cylinder intakeair (discharge intake air). This “control from the timing t3” isnitrogen enrichment control.

As shown in FIG. 4, through this nitrogen enrichment control, themembrane differential pressure (P5−P2) falls toward the target membranedifferential pressure Pd (=Ppump (negative pressure)−P1 (positivepressure)), and the concentration Od of oxygen in each of dischargeintake air and cylinder intake air falls toward the target oxygenconcentration Otg, from the timing t3. Furthermore, the membranedifferential pressure (P5−P2) coincides with the target membranedifferential pressure Pd, and the concentration Od of oxygen in each ofdischarge intake air and cylinder intake air coincides with the targetoxygen concentration Otg, at and after a timing t4. The foregoing is theoutline of the operation of the first gas supply device.

Next, the effect of the first gas supply device will be described. Thefirst gas supply device has more excellent effects, which will bedescribed below, than, for example, a typical gas supply device for aninternal combustion engine 200 according to a reference example (arelated art) of the present first embodiment of the disclosure shown inFIG. 7.

In the reference example, the intake air that has passed through theintercooler 46 is separated into oxygen-enriched air andnitrogen-enriched air in passing through the oxygen enrichment membranemodule 48. The oxygen-enriched air is stored into an oxygen tank 221,and the nitrogen-enriched air is stored into a nitrogen tank 222. An ECU(not shown) provided in the reference example performs oxygen enrichmentcontrol and nitrogen enrichment control, which will be described below,by sending signals to throttle valve actuators 211 b to 213 b andappropriately controlling the throttle valve opening degrees of anoxygen throttle valve 211 a, a nitrogen throttle valve 212 a, and an airthrottle valve 213 a. Incidentally, the throttle valve opening degreesof the throttle valves 211 a to 213 a are detected by the throttleopening degree sensors 211 c to 213 c respectively.

Next, a contrast between oxygen enrichment control according to thereference example and oxygen enrichment control of the first gas supplydevice will be described. In performing oxygen enrichment control, theECU according to the reference example sets the throttle valve openingdegree of the air throttle valve 213 a to “a predetermined throttlevalve opening degree (e.g., a more or less intermediate throttle valveopening degree)”, sets the throttle valve opening degree of the oxygenthrottle valve 211 a to “a throttle valve opening degree at the timewhen the oxygen throttle valve 211 a is fully open”, and sets thethrottle valve opening degree of the nitrogen throttle valve 212 a to “athrottle valve opening degree at the time when the nitrogen throttlevalve 212 a is fully closed”.

In this case, FIG. 8 shows examples of flow rates and compositions of“gases Fa1 to Fa3, a gas FN1, and a gas Fo1” shown in FIG. 7 andprescribed below. (i) The gas Fa1 is a gas passing through theintercooler 46 (the air passing through the intercooler). (ii) The gasFa2 is a gas branching off from the gas Fa1 and flowing into the oxygenenrichment membrane module 48 (the air passing through an oxygenseparation portion). (iii) The gas Fa3 is a gas branching off from thegas Fa1 and passing through the air throttle valve 213 a (the airpassing through a third valve). (iv) The gas FN1 is nitrogen-enrichedair obtained after separation of the gas Fa2 by the oxygen enrichmentmembrane module 48. (v) The gas Fo1 is oxygen-enriched air obtainedafter separation of the gas Fa2 by the oxygen enrichment membrane module48. Incidentally, as described previously, the opening degree of theoxygen throttle valve 211 a is a full-admission opening degree, and theopening degree of the nitrogen throttle valve 212 a is a full-closureopening degree. Therefore, the gas supplied into each of the cylinders22 is a gas (Fa3+Fo1) obtained by merging the gas Fa3 and the gas Fo1(oxygen-enriched air) with each other.

In FIG. 8, the leftmost bar chart corresponds to the air passing throughthe intercooler, the central bar chart corresponds to the air obtainedafter separation of the air passing through the intercooler into the airmoving toward the oxygen enrichment membrane module 48 and the airmoving toward the air throttle valve 213 a, and the rightmost bar chartcorresponds to the gas supplied to each of the cylinders 22 (the airflowing into the surge tank 42) and the gas discharged to theatmosphere.

As is understood from FIG. 8, in the reference example, the flow rate ofthe air Fa1 passing through the intercooler is much higher than “theflow rate of oxygen-enriched air (Fo1+Fa3) as the gas supplied to eachof the cylinders 22”. At the same time, the flow rate of the air Fa1passing through the intercooler is much higher than the flow rate of thegas FN1 discharged to the atmosphere. That is, when oxygen enrichmentcontrol is performed in the reference example, the flow rate of airpassing through the air cleaner 44 a, the intercooler 46 and thecompressor 45 a is very high. Accordingly, the air cleaner 44 a, theintercooler 46 and the compressor 45 a need to be enlarged in size.

Furthermore, in the reference example, only the compressor 45 a of theturbocharger 45 is used to pressurize intake air (pressurization forgenerating a membrane differential pressure in the oxygen enrichmentmembrane 48 b). Therefore, when the operating state of the internalcombustion engine 200 according to the reference example is a state (anon-supercharging state) where the compressor 45 a is substantially outof operation, the membrane differential pressure that is needed inseparating the gas Fa2 by the oxygen enrichment membrane module 48cannot be generated. Accordingly, when the operating state of theinternal combustion engine 200 is the non-supercharging state, theatmosphere cannot be reformed into oxygen-enriched air.

In contrast, in the first gas supply device, FIG. 9 shows examples offlow rates and compositions of “gases Fa11 and Fa12, a gas FN11, and agas Fo11” shown in FIG. 1 and prescribed below. (i) The gas Fa11 is thegas passing through the intercooler 46 (the air passing through theintercooler). (ii) The gas Fa12 is the gas passing through the rotarypump 62 (the air passing through the rotary pump). (iii) The gas FN11 isnitrogen-enriched air obtained after separation of the gas Fa12 by theoxygen enrichment membrane module 48. (iv) The gas Fo11 isoxygen-enriched air obtained after separation of the gas Fa12 by theoxygen enrichment membrane module 48. (v) The gas (Fa11+Fo11) obtainedby merging the gas Fa11 and the gas Fo11 with each other is the gassupplied into each of the cylinders 22.

In FIG. 9, which is a graph showing the composition, flow rate, andpressure of intake air and the like when the gas supply device for theinternal combustion engine according to the present first embodiment ofthe disclosure performs oxygen enrichment control, three bar charts inthe upper stage correspond, sequentially from the left to the right, tothe air passing through the rotary pump (i.e., the air that has not beenseparated into oxygen-enriched air and nitrogen-enriched air yet), theair that has been separated into oxygen-enriched air andnitrogen-enriched air, and the air discharged to the atmosphere,respectively. Furthermore, in FIG. 9, three bar charts in the lowerstage correspond, sequentially from the left to the right, to the airpassing through the intercooler, the air flowing into the oxygenenrichment membrane module 48, and the gas supplied to each of thecylinders 22 (the air flowing into the surge tank 42), respectively.

As is understood from FIG. 9, in the first gas supply device, the flowrate of the air Fa11 passing through the intercooler is lower than “theflow rate of oxygen-enriched air (Fa11+Fo11) as the gas supplied to eachof the cylinders 22”, in comparison with the foregoing referenceexample. That is, in the case where oxygen-enriched air is supplied toeach of the cylinders 22 at 100 (L/s) according to the foregoingreference example, the atmosphere needs to be pressurized at 180 (L/s)by the compressor 45 a. In contrast, in the case where oxygen-enrichedair is supplied to each of the cylinders 22 at 100 (L/s) by the firstgas supply device, the atmosphere may be pressurized only at 80 (L/s) bythe compressor 45 a. Accordingly, the first gas supply device can makethe air cleaner 44 a, the intercooler 46 and the compressor 45 a smallerin size than in the foregoing reference example.

Furthermore, in performing oxygen enrichment control, the first gassupply device generates a membrane differential pressure of the oxygenenrichment membrane 48 b that is needed in separating the gas Fa12 inthe oxygen enrichment membrane module 48, by operating (positivelyrotating) the rotary pump 62. Accordingly, even when the operating stateof the internal combustion engine 10 is the non-supercharging state, theatmosphere can be reformed into oxygen-enriched air.

Furthermore, in performing oxygen enrichment control, the first gassupply device sets the second throttle valve opening degree TA2 to “thesecond full-admission opening degree”, and sets the first throttle valveopening degree TA1 to “a throttle valve opening degree TAim for makingthe pressure P2 coincide with the target intake pressure Pim2”. Thus,the pressure in the intra-membrane space becomes negative. Accordingly,the membrane differential pressure Pd can be efficiently made high evenwhen the pressure in the extra-membrane space (the pressure P5 ofauxiliary air, namely, the target pump pressure Ppump) is not made veryhigh. As a result, the air containing a high concentration of oxygen canbe introduced into the intra-membrane space without making the energyconsumed by the rotary pump 62 large. Thus, oxygen-enriched air can beproduced with good energy efficiency.

Next, a contrast between nitrogen enrichment control according to theforegoing reference example and nitrogen enrichment control of the firstgas supply device will be described. In performing nitrogen enrichmentcontrol, the ECU according to the foregoing reference example sets thethrottle valve opening degree of the air throttle valve 213 a to “thethrottle valve opening degree at the time when the air throttle valve213 a is fully closed”, sets the throttle valve opening degree of theoxygen throttle valve 211 a to “the throttle valve opening degree at thetime when the oxygen throttle valve 211 a is fully closed”, and sets thethrottle valve opening degree of the nitrogen throttle valve 212 a to“the predetermined throttle valve opening degree (e.g., the more or lessintermediate throttle valve opening degree)”.

In this case, FIG. 10 shows examples of flow rates and compositions of“a gas Fa21, a gas Fo21, and a gas FN21” shown in FIG. 7 and prescribedbelow. (i) The gas Fa21 is the gas passing through the intercooler 46(the air passing through the intercooler). (ii) The gas FN21 isnitrogen-enriched air obtained after separation of the gas Fa21 by theoxygen enrichment membrane module 48. (iii) The gas Fo21 isoxygen-enriched air obtained after separation of the gas Fa21 by theoxygen enrichment membrane module 48. Incidentally, as describedpreviously, the opening degree of the oxygen throttle valve 211 a isequal to the full-closure opening degree, and the opening degree of theair throttle valve 213 a is also equal to the full-closure openingdegree. Therefore, the gas supplied into each of the cylinders 22 is thegas FN21 (nitrogen-enriched air).

In FIG. 10, the leftmost bar chart corresponds to the air passingthrough the intercooler, the central bar chart corresponds to the airobtained after separation of the air passing through the intercoolerinto the air moving toward the oxygen enrichment membrane module 48 andthe air moving toward the air throttle valve 213 a, and the rightmostbar chart corresponds to the gas supplied to each of the cylinders 22(the air flowing into the surge tank 42) and the gas discharged to theatmosphere.

In contrast, in the first gas supply device, FIG. 11 shows examples offlow rates and compositions of “a gas Fa31, a gas Fo31, and a gas FN31”shown in FIG. 1 and prescribed below. (i) The gas Fa31 is the gaspassing through the intercooler 46 (the air passing through theintercooler). (ii) The gas Fo31 is oxygen-enriched air obtained afterseparation of the gas Fa31 by the oxygen enrichment membrane module 48.(iii) The gas FN31 is nitrogen-enriched air obtained after separation ofthe gas Fa31 by the oxygen enrichment membrane module 48, and is the gassupplied to each of the cylinders 22.

In FIG. 11, the leftmost bar chart corresponds to the air passingthrough the intercooler, the central bar chart corresponds to the airobtained after separation of the air passing through the intercooler bythe oxygen enrichment membrane module 48, and the rightmost bar chartcorresponds to the gas supplied to each of the cylinders 22 (the airflowing into the surge tank 42) and the gas discharged to theatmosphere.

As is understood from a comparison between FIG. 10 and FIG. 11, there isno difference in the flow rate and composition of the gases between thereference example and the first gas supply device, when nitrogenenrichment control is performed.

In the foregoing reference example, however, only the compressor 45 a ofthe turbocharger 45 is used to pressurize intake air (pressurization forgenerating the membrane differential pressure of the oxygen enrichmentmembrane 48 b). Therefore, when the operating state of the internalcombustion engine 200 is the non-supercharging state, the membranedifferential pressure that is needed in separating the gas Fa21 by theoxygen enrichment membrane module 48 cannot be generated. Accordingly,when the operating state of the internal combustion engine 200 is thenon-supercharging state, the atmosphere cannot be reformed intonitrogen-enriched air.

In contrast, in performing nitrogen enrichment control, the first gassupply device generates the membrane differential pressure of the oxygenenrichment membrane 48 b that is needed in separating the gas Fa31 bythe oxygen enrichment membrane module 48, by operating (reverselyrotating) the rotary pump 62. Accordingly, even when the operating stateof the internal combustion engine 10 is the non-supercharging state, theatmosphere can be reformed into nitrogen-enriched air.

Furthermore, in performing nitrogen enrichment control, the first gassupply device sets the first throttle valve opening degree TA1 to “thefirst full-admission opening degree”, and sets the second throttle valveopening degree TA2 to “the throttle valve opening degree TAim for makingthe pressure P4 coincide with the target intake pressure Pim4”.Accordingly, the pressure in the intra-membrane space is equal to theatmospheric pressure, or higher than the atmospheric pressure whensupercharging is carried out. In consequence, the membrane differentialpressure Pd can be efficiently made high even when the pressure in theextra-membrane space (the pressure of auxiliary air P5, namely, thetarget pump pressure Ppump) is not made very low. As a result, the aircontaining a high concentration of nitrogen (nitrogen-enriched air) canbe produced in the intra-membrane space with good energy efficiency,without making the energy consumed by the rotary pump 62 large.

Next, the concrete operation performed by the first gas supply devicewill be described. The CPU of the ECU 70 (hereinafter referred to simplyas “the CPU”) executes a routine indicated by a flowchart of FIG. 12, atintervals of a predetermined time.

The CPU starts a process in step 1200 at a predetermined timing,sequentially carries out processes in steps 1205 to 1210 that will bedescribed below, and then proceeds to step 1215.

In step 1205, the CPU acquires a concentration of oxygen (the detectedoxygen concentration Oair) in air (fresh air or the atmosphere) detectedby the oxygen concentration sensor 76.

In step 1207, the CPU determines the target oxygen concentration Otgfrom the operating state of the internal combustion engine 10. Inconcrete terms, if cold start of the engine has just ended (when thecooling liquid temperature THW is lower than a liquid temperatureTHWth), the CPU sets the target oxygen concentration Otg to “an oxygenconcentration (a high oxygen concentration) selected from a range higherthan 21% and equal to or lower than 26%” with a view to warming up acatalyst at an early stage. If the engine has been warmed up (when thecooling liquid temperature THW is equal to or higher than the liquidtemperature THWth), the CPU sets the target oxygen concentration Otg to“an oxygen concentration (a low oxygen concentration) selected from arange equal to or higher than 16% and lower than 21%” with a view toimproving fuel economy. Incidentally, the concentration of oxygen in theatmosphere is equal to 21%.In step 1210, the CPU determines the target intake pressure Pim byapplying the engine rotational speed NE and the in-cylinder requestedintake air flow rate to a look-up table (referred to also as “a map”) M1indicated by a block B11. Incidentally, the CPU separately calculatesthe in-cylinder requested intake air flow rate by applying the enginerotational speed NE acquired from the engine rotational speed sensor 77and the accelerator pedal operation amount AP acquired from theaccelerator pedal operation amount sensor 79 to a look-up table (notshown).

Upon proceeding to step 1215, the CPU determines whether or not thedetected oxygen concentration Oair and the target oxygen concentrationOtg are equal to each other.

If the detected oxygen concentration Oair and the target oxygenconcentration Otg are equal to each other, the CPU determines that theresult of step 1215 is “Yes”, sequentially carries out processes ofsteps 1220 to 1230 that will be described below, and then proceeds tostep 1295 to temporarily end the present routine. Thus, the foregoingnormal control is performed.

In step 1220, the CPU sends a signal to the first throttle valveactuator 47 b, and sets the first throttle valve opening degree TA1 tothe first full-admission opening degree. In step 1225, the CPU sets thesecond throttle valve opening degree TA2 to the throttle valve openingdegree TAim corresponding to the target intake pressure Pim determinedin step 1210. That is, the CPU sends a signal to the second throttlevalve actuator 49 b, and controls the second throttle valve openingdegree TA2 such that the pressure P4 of intake air detected by theintake pipe pressure sensor 75 d coincides with the target intakepressure Pim4 (=Pim). In step 1230, the CPU stops the rotary pump 62.Incidentally, if the rotary pump 62 is stopped at the time point of thisprocess, the CPU holds the rotary pump 62 stopped. Incidentally, whenthe CPU performs normal control, the pressure applied to the check valve63 is lower than the predetermined valve-opening pressure, so the checkvalve is closed.

In contrast, if the detected oxygen concentration Oair and the targetoxygen concentration Otg are different from each other, the CPUdetermines that the result of step 1215 is “No”, and proceeds to step1235 to determine whether or not the detected oxygen concentration Oairis lower than the target oxygen concentration Otg.

If the detected oxygen concentration Oair is lower than the targetoxygen concentration Otg, the CPU determines that the result of step1235 is “Yes”, sequentially carries out processes in steps 1240 to 1255that will be described below, and then proceeds to step 1295 totemporarily end the present routine. Thus, the foregoing oxygenenrichment control is performed.

In step 1240, the CPU determines the target membrane differentialpressure Pd by applying the target oxygen concentration Otg and theseparately calculated in-cylinder requested intake air flow rate to alook-up table M2 indicated by a block B12.

In step 1245, the CPU operates (positively rotates) the rotary pump 62such that the pressure P4 of auxiliary air pressurized by the rotarypump 62 (the pressure detected by the auxiliary conduit pressure sensor75 e) coincides with a pressure (Pim+Pd) obtained by summating thetarget intake pressure Pim and the target membrane differential pressurePd.In step 1250, the CPU sends a signal to the second throttle valveactuator 49 b, and sets the second throttle valve opening degree TA2 tothe second full-admission opening degree.In step 1255, the CPU sends a signal to the first throttle valveactuator 47 b, and sets the first throttle valve opening degree TA1 to“the throttle valve opening degree TAim corresponding to the targetintake pressure Pim determined in step 1210”. That is, the CPU controlsthe first throttle valve opening degree TA1 such that the pressure P2 ofintake air detected by the intake pipe pressure sensor 75 b coincideswith the target intake pressure Pim2 (=Pim).Incidentally, if the pressure in the extra-membrane space is higher thanthe predetermined valve-opening pressure of the check valve 63 whenoxygen enrichment control is performed, the check valve 63 is open. Ifthe pressure in the extra-membrane space is equal to or lower than thepredetermined valve-opening pressure of the check valve 63, the checkvalve 63 is closed.

In contrast, if the detected oxygen concentration Oair is equal to orhigher than the target oxygen concentration Otg, the CPU determines thatthe result of step 1235 is “No”, sequentially carries out processes insteps 1260 to 1275 that will be described later, and then proceeds tostep 1295 to temporarily end the present routine. Thus, the foregoingnitrogen enrichment control is performed.

In step 1260, the CPU determines the target membrane differentialpressure Pd by applying the target oxygen concentration Otg and theseparately calculated in-cylinder requested intake air flow rate to thelook-up table M2 indicated by the block B12.

In step 1265, the CPU operates (reversely rotates) the rotary pump 62such that the pressure P4 of auxiliary air depressurized by the rotarypump 62 coincides with a pressure (P1+Pd) obtained by summating thepressure P1 immediately behind the intercooler 46 detected by the intakepipe pressure sensor 75 a and the target membrane differential pressurePd.In step 1270, the CPU sends a signal to the first throttle valveactuator 47 b, and sets the first throttle valve opening degree TA1 tothe first full-admission opening degree.In step 1275, the CPU sends a signal to the second throttle valveactuator 49 b, and sets the second throttle valve opening degree TA2 tothe throttle valve opening degree TAim corresponding to the targetintake pressure Pim determined in step 1210. That is, the CPU controlsthe second throttle valve opening degree TA2 such that the pressure P4of intake air detected by the intake pipe pressure sensor 75 d coincideswith the target intake pressure Pim4 (=Pim). Incidentally, when nitrogenenrichment control is performed, the pressure applied to the check valve63 is lower than the predetermined valve-opening pressure, so the checkvalve 63 is closed.

According to the first gas supply device, an effect that will bedescribed below can be obtained. That is, the first gas supply devicegenerates the membrane differential pressure of the oxygen enrichmentmembrane 48 b that is needed in separating gas by the oxygen enrichmentmembrane module 48, through the use of the rotary pump 62, in performingoxygen enrichment control or nitrogen enrichment control. Accordingly,even when the operating state of the internal combustion engine 10 isthe non-supercharging state, the air can be reformed intooxygen-enriched air or nitrogen-enriched air.

Next, a gas supply device according to the second embodiment of thedisclosure (hereinafter referred to as “a second gas supply device” insome cases) will be described. This second gas supply device isdifferent from the first gas supply device only in the followingrespect.

As shown in FIG. 13, the second gas supply device is obtained byadditionally providing the first gas supply device with a normal airintake pipe 90, and a third throttle valve 81 a and third throttle valveactuator 81 b that are disposed in the normal air intake pipe 90. Thenormal air intake pipe 90 constitutes an air passage through whichintake air passes, between the intercooler 46 and a region downstream ofthe first throttle valve 47 a, and establishes communication between aregion downstream of the second throttle valve 49 a and a regionupstream of the surge tank 42.The third throttle valve actuator 81 b includes a third throttle openingdegree sensor 81 c for detecting a third throttle valve opening degree.The third throttle opening degree sensor 81 c detects the third throttlevalve opening degree of the third throttle valve 81 a, and outputs asignal representing a third throttle valve opening degree TA3 to the ECU70. Incidentally, the normal air intake pipe 90 will be referred to alsoas “a fifth pipe portion” for the sake of convenience, and the airpassage thereof will be referred to also as “a fifth air passage”. Thethird throttle valve 81 a will be referred to also as “a third valve”for the sake of convenience, and the throttle valve opening degreethereof will be referred to also as “a third valve opening degree”.When there is a request to supply normal air into each of the cylinders22 (i.e., when normal control is performed), the second gas supplydevice sets the throttle valve opening degrees of the first throttlevalve 47 a, the second throttle valve 49 a, and the third throttle valve81 a as will be described below. Thus, the second gas supply devicesupplies the intake air that has passed through the intercooler 46 intoeach of the cylinders 22 through the normal air intake pipe 90, withoutthe intermediary of the oxygen enrichment membrane module 48.The first throttle valve opening degree TA1 of the first throttle valve47 a is a throttle valve opening degree at the time when the firstthrottle valve 47 a is fully closed.The second throttle valve opening degree TA2 of the second throttlevalve 49 a is a throttle valve opening degree at the time when thesecond throttle valve 49 a is fully closed.The third throttle valve opening degree TA3 of the third throttle valve81 a is the throttle valve opening degree TAim corresponding to thetarget intake pressure Pim (i.e., the throttle valve opening degree formaking the pressure P4 coincide with the target intake pressure Pim4(=Pim)).Incidentally, the second gas supply device is the same as the first gassupply device except that the third throttle valve opening degree of thethird throttle valve 81 a is set to the throttle valve opening degree atthe time when the third throttle valve 81 a is fully closed, inperforming oxygen enrichment control and nitrogen enrichment control.

As is the case with the first gas supply device, the second gas supplydevice thus configured can reform air into oxygen-enriched air ornitrogen-enriched air and can efficiently reform air intooxygen-enriched air or nitrogen-enriched air, even when the operatingstate of the internal combustion engine 10 is the non-superchargingstate.

Furthermore, in performing normal control, the second gas supply devicecan supply the intake air that has passed through the intercooler 46into each of the cylinders 22, without the intermediary of the oxygenenrichment membrane module 48. Accordingly, the second gas supply devicecan prevent the occurrence of pressure loss at the time of passagethrough the oxygen enrichment membrane module 48, in performing normalcontrol.

Next, a gas supply device according to the third embodiment of thedisclosure (hereinafter referred to as “a third gas supply device” insome cases) will be described. This third gas supply device is differentfrom the first gas supply device only in the following respect.Incidentally, the characteristics of the third gas supply device canalso be applied to the second gas supply device. As shown in FIG. 14,the third gas supply device is obtained by additionally providing thefirst gas supply device with an exhaust gas recirculation pipe (an EGRpipe) 100, an EGR valve 101 a, an EGR valve actuator 101 b, and an EGRcooler (an EGR gas cooling device) 102.

The exhaust gas recirculation pipe 100 constitutes an EGR gas passagethrough which EGR gas flows. One end of the exhaust gas recirculationpipe 100 communicates with the second air passage between a regiondownstream of the second throttle valve 49 a and a region upstream ofthe surge tank 42. The other end of the exhaust gas recirculation pipe100 communicates with the exhaust manifold 51 of the exhaust passage.

The EGR valve actuator 101 b includes an EGR valve opening degree sensor101 c. The EGR valve opening degree sensor 101 c is connected to the ECU70, detects an EGR valve opening degree of the EGR valve 101 a, andoutputs a signal representing an EGR valve opening degree TAegr. The EGRvalve 101 a is disposed in the exhaust gas recirculation pipe 100. TheEGR valve 101 a adjusts the amount of EGR gas flowing through theexhaust gas recirculation pipe 100, in response to a command of the ECU70.

The EGR cooler 102 is disposed in the exhaust gas recirculation pipe 100at a position upstream of the EGR valve 101 a in a flow direction of EGRgas. The EGR cooler 102 lowers the temperature of EGR gas. The EGR valve101 a adjusts the amount of EGR gas passing through the EGR gas passage,by making the opening cross-sectional area of the EGR gas passagevariable. The EGR valve actuator 91 b changes the EGR valve openingdegree TAegr of the EGR valve 101 a in accordance with the command ofthe ECU 70. The third gas supply device opens the EGR valve 101 a andsupplies EGR gas to the intake pipe 43, in performing each of nitrogenenrichment control and oxygen enrichment control.

As is the case with the first gas supply device, the third gas supplydevice thus configured can reform intake air into oxygen-enriched air ornitrogen-enriched air and can efficiently reform intake air intooxygen-enriched air or nitrogen-enriched air, even when the operatingstate of the internal combustion engine 10 is in a non-superchargingrange.

Furthermore, the third gas supply device can supply EGR gas into each ofthe cylinders 22 (each of the combustion chambers) in performingnitrogen enrichment control. Accordingly, the third gas supply devicecan further lower the concentration of oxygen in the gas supplied toeach of the cylinders 22 during nitrogen enrichment control. As aresult, the third gas supply device can improve fuel economy and reducethe amount of NOx. Furthermore, the third gas supply device can alsosupply EGR gas into each of the combustion chambers of the cylinders 22in performing oxygen enrichment control. In this case, the nitrogencontained in the gas supplied to each of the cylinders 22 is replacedwith EGR gas. In consequence, the specific heat of intake air rises, andthe temperature of combustion can be lowered, so the amount of NOx canbe reduced.

Although the respective embodiments of the disclosure have beendescribed above concretely, the disclosure is not limited to theabove-mentioned respective embodiments thereof, but can be modified invarious manners based on the technical concept thereof.

For example, each of the first to third gas supply devices may employ adiaphragm pump or a piston pump instead of the rotary pump 62. Each ofthe first to third gas supply devices may employ a throttle valveinstead of the check valve and control the throttle valve opening degreeof the throttle valve such that the throttle valve performs the sameoperation as the check valve.

For example, when a changeover between pressurization anddepressurization cannot be made by positively or reversely rotating therotary pump, each of the first to third gas supply devices may changeover piping connection and the valves or include two or more rotarypumps installed therein.

For example, in each of the first to third gas supply devices, theoxygen enrichment membrane module is not absolutely required to use ahollow fiber-like oxygen enrichment membrane, as long as air can beseparated into oxygen-enriched air and nitrogen-enriched air. That is,various oxygen enrichment membrane modules can be employed. For example,the oxygen enrichment membrane module employed in each of the first tothird gas supply devices may include a module structure such as a flatmembrane laminated-type structure, a honeycomb monolith-type structureor the like.

What is claimed is:
 1. A gas supply device for an internal combustionengine, the gas supply device comprising: an oxygen enrichment membranemodule that includes a housing and an oxygen enrichment membrane, aspace in the housing being separated into a first space and a secondspace by the oxygen enrichment membrane; a first pipe portion thatconstitutes a first air passage including one end from which anatmosphere can flow into the one end and the other end whichcommunicates with the first space; a second pipe portion thatconstitutes a second air passage including one end which communicateswith the first space and the other end which communicates with acombustion chamber of the internal combustion engine; a pump portionthat is configured to raise a pressure in the second space by supplyinga high-pressure atmosphere to the second space, and that is configuredto lower the pressure in the second space by discharging air in thesecond space to an outside of the housing from the second space; and anelectronic control unit that is configured to: (i) control a drive stateof the pump portion, (ii) supply air to the first space from the secondspace through the oxygen enrichment membrane, by supplying thehigh-pressure atmosphere to the second space by driving the pump portionsuch that the pressure in the second space rises, a concentration ofoxygen of the air being higher than a concentration of oxygen of theatmosphere, (iii) perform oxygen enrichment control that merges the airsupplied to the first space with the atmosphere that has flowed into thefirst space through the first air passage, and supplies the merged airand atmosphere to the combustion chamber through the second air passage,the concentration of oxygen of the air being higher than theconcentration of oxygen of the atmosphere, and (iv) perform nitrogenenrichment control that discharges air to the second space from thefirst space through the oxygen enrichment membrane, a concentration ofoxygen of the air being higher than a concentration of oxygen of theatmosphere, produces air in the first space, a concentration of nitrogenof the air being higher than a concentration of nitrogen of theatmosphere, and supplies the air containing the higher concentration ofnitrogen to the combustion chamber through the second air passage, bydischarging the air in the second space to the outside of the housingfrom the second space by driving the pump portion such that the pressurein the second space falls.
 2. The gas supply device for the internalcombustion engine according to claim 1, wherein the housing includes afirst communication hole and a second communication hole, the firstcommunication hole connecting the first space to the other end of thefirst air passage, the second communication hole connecting the firstspace to the one end of the second air passage, and the firstcommunication hole and the second communication hole being provided atpositions that are opposed to each other, the first pipe portion isconnected to the housing such that the other end of the first airpassage communicates with the first communication hole, and the secondpipe portion is connected to the housing such that the one end of thesecond air passage communicates with the second communication hole. 3.The gas supply device for the internal combustion engine according toclaim 2, the gas supply device further comprising: a check valve that isconfigured to discharge the air in the second space to the outside ofthe housing by opening when the pressure in the second space becomesequal to or higher than a predetermined valve-opening pressure.
 4. Thegas supply device for the internal combustion engine according to claim3, the gas supply device further comprising: a third pipe portion thatconstitutes a third air passage, one end of the third air passage beingconnected to the pump portion; and a fourth pipe portion thatconstitutes a fourth air passage that is opened and closed by the checkvalve, wherein the housing is equipped with a third communication holethat establishes communication between the second space and the thirdair passage, and a fourth communication hole that establishescommunication between the second space and the fourth air passage, thethird communication hole and the fourth communication hole beingprovided at positions that are opposed to each other, the third pipeportion is connected to the housing such that the other end of the thirdair passage communicates with the third communication hole, and thefourth pipe portion is connected to the housing such that the fourth airpassage communicates with the fourth communication hole.
 5. The gassupply device for the internal combustion engine according to claim 4,wherein the oxygen enrichment membrane assumes a shape of a hollow tubewith both end surfaces of the hollow tube open, and is disposed in sucha manner as to connect the first communication hole and the secondcommunication hole to each other, a space inside the oxygen enrichmentmembrane constitutes the first space, a space other than the first spacein the housing constitutes the second space, and the housing is providedwith the first communication hole, the second communication hole, thethird communication hole, and the fourth communication hole such that adirection in which the third communication hole and the fourthcommunication hole are linked with each other becomes parallel to asurface perpendicular to a direction in which the first communicationhole and the second communication hole are linked with each other. 6.The gas supply device for the internal combustion engine according toclaim 1, the gas supply device further comprising: a compressor of asupercharger of the internal combustion engine that is disposed in thefirst pipe portion; a first throttle valve that is disposed in the firstpipe portion between the compressor and the oxygen enrichment membranemodule and that is configured to change a passage cross-sectional areaof the first air passage through a change in opening degree of the firstthrottle valve; and a second throttle valve that is disposed in thesecond pipe portion between the oxygen enrichment membrane module andthe combustion chamber of the internal combustion engine and that isconfigured to change a passage cross-sectional area of the second airpassage through a change in opening degree of the second throttle valve,wherein the electronic control unit is configured to: in performing theoxygen enrichment control, (i) change the opening degree of the firstthrottle valve in accordance with an in-cylinder requested intake airflow rate as a flow rate of air requested of the combustion chamber ofthe internal combustion engine, and (ii) set the opening degree of thesecond throttle valve to an opening degree at a time when the secondthrottle valve is fully open, and the electronic control unit isconfigured to: in performing the nitrogen enrichment control, (i) setthe opening degree of the first throttle valve to an opening degree at atime when the first throttle valve is fully open, and (ii) change theopening degree of the second throttle valve in accordance with thein-cylinder requested intake air flow rate.
 7. The gas supply device forthe internal combustion engine according to claim 6, wherein theelectronic control unit is configured to: (i) stop driving the pumpportion, (ii) set the opening degree of the first throttle valve to theopening degree at the time when the first throttle valve is fully open,(iii) change the opening degree of the second throttle valve inaccordance with the in-cylinder requested intake air flow rate, and (iv)perform normal control for supplying the air flowing into the firstspace from the first air passage to the combustion chamber through thesecond air passage, without reforming the air.
 8. The gas supply devicefor the internal combustion engine according to claim 7, the gas supplydevice further comprising: a fifth pipe portion that constitutes a fifthair passage including one end that communicates with a location betweenthe compressor in the first air passage and the first throttle valve andthe other end that communicates with a location between the secondthrottle valve in the second air passage and the communication chamber;and a third throttle valve that is disposed in the fifth pipe portionand that changes a passage cross-sectional area of the fifth air passagethrough a change in opening degree of the third throttle valve, whereinthe electronic control unit is configured to set the opening degree ofthe third throttle valve to an opening degree at a time when the thirdthrottle valve is fully closed, in performing the oxygen enrichmentcontrol or the nitrogen enrichment control, and the electronic controlunit is configured to change the opening degree of the third throttlevalve in accordance with the in-cylinder requested intake air flow rate,in performing the normal control.
 9. A control method for a gas supplydevice for an internal combustion engine, the gas supply deviceincluding: an oxygen enrichment membrane module that includes a housingand an oxygen enrichment membrane, a space in the housing beingseparated into a first space and a second space by the oxygen enrichmentmembrane, a first pipe portion that constitutes a first air passageincluding one end from which an atmosphere can flow into the one end andthe other end which communicates with the first space, a second pipeportion that constitutes a second air passage including one end whichcommunicates with the first space and the other end which communicateswith a combustion chamber of the internal combustion engine, and a pumpportion that is configured to raise a pressure in the second space bysupplying a high-pressure atmosphere to the second space, and that isconfigured to lower the pressure in the second space by discharging airin the second space to an outside of the housing from the second space,the control method comprising: (i) controlling a drive state of the pumpportion; (ii) supplying air to the first space from the second spacethrough the oxygen enrichment membrane, by supplying the high-pressureatmosphere to the second space by driving the pump portion such that thepressure in the second space rises, a concentration of oxygen of the airbeing higher than a concentration of oxygen of the atmosphere; (iii)performing oxygen enrichment control that merges the air supplied to thefirst space with the atmosphere that has flowed into the first spacethrough the first air passage, and supplies the merged air andatmosphere to the combustion chamber through the second air passage, theconcentration of oxygen of the air being higher than the concentrationof oxygen of the atmosphere; and (iv) performing nitrogen enrichmentcontrol that discharges air to the second space from the first spacethrough the oxygen enrichment membrane, a concentration of oxygen of theair being higher than a concentration of oxygen of the atmosphere,produces air in the first space, a concentration of nitrogen of the airbeing higher than a concentration of nitrogen of the atmosphere, andsupplies the air containing the higher concentration of nitrogen to thecombustion chamber through the second air passage, by discharging theair in the second space to the outside of the housing from the secondspace by driving the pump portion such that the pressure in the secondspace falls.